The present invention generally relates to turbomachinery, and more particularly to anti-icing and de-icing systems for aircraft engine surfaces.
FIG. 1 schematically represents a high-bypass turbofan engine 10 of a type known in the art. The engine 10 is schematically represented as including a fan assembly 12 and a core engine 14. The fan assembly 12 is shown as including a composite fan casing 16 and a spinner nose 20 projecting forward from an array of fan blades 18. Both the spinner nose 20 and fan blades 18 are supported by a fan disc (not shown). The core engine 14 is represented as including a high-pressure compressor 22, a combustor 24, a high-pressure turbine 26 and a low-pressure turbine 28. A large portion of the air that enters the fan assembly 12 is bypassed to the rear of the engine 10 to generate additional engine thrust. The bypassed air passes through an annular-shaped bypass duct 30 and exits the duct 30 through a fan nozzle 32. The fan blades 18 are surrounded by a fan nacelle 34 that defines a radially outward boundary of the bypass duct 30, as well as an inlet duct 36 to the engine 10 and the fan nozzle 32. The core engine 14 is surrounded by a core cowl 38 that defines the radially inward boundary of the bypass duct 30, as well as an exhaust nozzle 40 that extends aftward from the core engine 14.
The fan nacelle 34 is an important structural component whose design considerations include aerodynamic criteria as well as the ability to withstand foreign object damage (FOD). For these reasons, it is important to select appropriate constructions, materials and assembly methods when manufacturing the nacelle 34. Various materials and configurations have been considered, with metallic materials and particularly aluminum alloys being widely used. Composite materials have also been considered, such as epoxy laminates reinforced with carbon (graphite) fibers or fabrics, as they offer advantages including the ability to be fabricated as single-piece parts of sufficient size to meet aerodynamic criteria, contour control, and reduced weight, which promote engine efficiency and improve specific fuel consumption (SFC).
Aircraft engine nacelles are subject to icing conditions, particularly the nacelle leading edge at the inlet lip (42 of FIG. 1) while the engine is on the ground and especially under flight conditions. One well known approach to removing ice buildup (de-icing) and preventing ice buildup (anti-icing) on the nacelle inlet lip 42 has been through the use of hot air bleed systems. As an example, engine-supplied bleed air can be drawn from the combustion chamber 24 through piping (not shown) to the inlet lip 42, where the hot bleed air contacts the internal surface of the inlet lip 42 to heat the lip 42 and remove/prevent ice formation. As an alternative, some smaller turboshaft and turboprop aircraft engines have utilized electrical anti-icing systems that convert electrical energy into heat via Joule heating. Resistance-type heater wires can be used as the heating element, though a more recent example uses a flexible graphite material. The heating element is embedded in a boot, such as a silicon rubber, which in turn is attached to the inside leading edge of the nacelle inlet lip 42. A drawback of such systems is that they may require excessive energy for de-icing and continuous anti-icing operation on large aircraft engines, such as high-bypass turbofan engines of the type represented in FIG. 1.
Still other options include “weeping” systems that release chemical de-icing agents, and de-icing boots equipped with inflatable bladders to crack ice buildup. Notable disadvantages of weeping systems include the high cost of chemical de-icing agents, the requirement that the aircraft carry the de-icing agent at all times, and the inoperability of the system if the supply of chemical agent is exhausted during flight. Disadvantages of de-icing boots include the requirement for a pump to inflate the bladders and a relatively short life span.
In view of the above, there are ongoing efforts to develop new technologies capable of providing de-icing and anti-icing functions with improved thermal transfer to the protected surfaces.